Confused with Tutorial 4, Perspective Projection

Which is at (0, 0, 0) in camera space - the camera, or the center of the projection plane?

The tutorial says that "the location of the center of the perspective plane is fixed at (0, 0, -1) in camera space. Therefore, since the projection plane is pointing down the -Z axis, eye's location relative to the plane of projection is (0, 0, -1)." If the eye is pointing down the -Z axis and the eye is at (0, 0, 0), then shouldn't the eye's location relative to the projection plane be (0, 0, 1)?

Later, the tutorial says "The eye is fixed at (0, 0, -1)." What's the right position?